Multi-zone incipient or actual fire and/or dangerous gas detection system

ABSTRACT

A multi-zone detecting system for incipient or actual fires and/or dangerous gas accumulations comprising a multi-zone sampling system for obtaining samples of the atmosphere of the respective zones being monitored and supplying the same to a common sampling station. The sample gases are continuously drawn off and supplied through a rotary selector valve sequentially to the input of a common condensation nuclei particle detector located at the common sampling station. The sensitivity of the condensation nuclei detector is individually adjusted in synchronism with the operation of the rotary selector valve to adjust the sensitivity of the condensation nuclei detector to the individual background conditions existing in each zone being monitored as the detector is sequentially switched from one zone to the next. The sensitivity of the common condensation nuclei detector is decreased for a predetermined short time settling interval following each sequential switching operation prior to making a measurement with respect to the sample atmosphere of the new zone to which it is switched. A gas conversion device can be interposed in the input to the common condensation nuclei detector for converting certain dangerous gases that might be entrained in the sample atmospheres from the several zones into condensation nuclei for supply and analysis by the condensation nuclei detector. With such an arrangement, the concentration of condensation nuclei particles detected would be in proportion to the dangerous gas constituency of the sample atmospheres. A continuous flow sample system provides a relatively fast responding detection of the occurrence of an alarm condition in any of the several zones being monitored. Additional advantageous features are described.

O United States Patent [151 3,6 Ludewlg, Jr. et al. 1451 July 18, 1972MULTl-ZONE INCIPIENT 0R ACTUAL and/or dangerous gas accumulationscomprising a multi-zone FIRE AND/0R DANGEROUS GAS sampling system forobtaining samples of the atmosphere of DETECTION SYST M the respectivezones being monitored and supplying the same to a common samplingstation. The sample gases are continu- [72] inventors: Frederick A.Ludewig, Jr., Ballston Spa; ously drawn off and supplied through arotary selector valve M VIII Lllik, J h nect y. sequentially to theinput of a common condensation nuclei both of particle detector locatedat the common sampling station. The sensitivity of the condensationnuclei detector is individually [73] Assume gam Corn-mm scheme adjustedin synchronism with the operation of the rotary selector valve to adjustthe sensitivity of the condensation nuclei Filed! 1971 detector to theindividual background conditions existing in each zone bein monitored asthe detector is se uentiall [21] Appl' switched from ne zone to thenext. The sensitivi ty of mi common condensation nuclei detector isdecreased for a [52] [1.8. CI ..340/236, 73/432 PS, 356/37 predeterminedshort time settling interval following each 5 1] Int. Cl. ..G08b 19/00sequential switching operation prior to making a measurement [58] FieldoiSearch ..73/23, 29, 432 PS; 235/151, with respect to the sampleatmosphere of the new zone to 235/ l5l.3, 151.34; 340/236; 356/37 whichit is switched. A gas conversion device can be interposed in the inputto the common condensation nuclei detec- References Cited tor forconverting certain dangerous gases that might be entrained in the sampleatmospheres from the several zones into UNITED STATES PATENTScondensation nuclei for supply and analysis by the condensa- 3,588,48l6/197] St Nuns/151.34 tion nuclei detector. With such an arrangement,the concen- 3,618,06l 11/1971 Livers ..340/236 ration of condensationnuclei timides deleced would be in Primary Examiner-Donald J. YuskoAttorney-Charles We Helzer [57] ABSTRACT A multi-zone detecting systemfor incipient or actual fires proportion to the dangerous gasconstituency of the sample atmospheres. A continuous flow sample systemprovides a relatively fast responding detection of the occurrence of analarm condition in any of the several zones being monitored. Additionaladvantageous features are described.

34 Claims, 3 Drawing Figures FIRE DETECTOR BLOCK DlAGRAM [GAS "muss mom4 2011155 1 ZONEI 201i 2 201: 3 zone 4 m Bil" 1 131 'II a I l m MR I30Bb 1311 I31: l3c I3d DETECTORS 7 SAMPLING '20 Am SELECTOR BLOWER g0 M M(P (1 H v M VALVE AND L SWITCHING v a v2 d v3 1 7 EGG 3a 1 1 1) ,L 1 v w270 1? J l? 25 F Ms K 221 m cm T 32 couvznsmn E 09mm um a nuts svmcnzs111 vacuum Yr 1.

27b 7 A v 24 1 PUMP 1 Y{*-* CLOUD CHAMBER mmmsnr VALVE ASSEMBLY W65 I I9'7 CHANGE cu wsmms cmcun 21 I 7 5 sec. ALARM ALARM a DELAY SIGNALMLFUNCT'O" zone lnsmlncmou new cmcunm' PATE'NTEDJRL I8 I972 SHEET 1 (IF3 FIRE DETECTOR BLDCK DIAGRAM GAS INTAKES FROM 4 ZONES I ME I 20m: 2ZONE 3 ZONE 4 no" l3d" m R??? WE A|R :36" I311 Lib 13c 136'" |3d O Q Q)oETEcmRs SAMPLING f f f I20 |2| |2c |2a AIR SELECTOR BLOWER (I) Al A2 (I(I? A3 v M vALvE Ann I 3 SWITCHING VI V2 V3 V CAMS v 260 J I M ,L 1 l V12 0 I7 J a 1 I GAS E1 23 cm I 22 I CONVERSION OPERATED umr a FILTERSWITCHES vAcuuM L E" L 5 27b 7 24,-'\ PUMP LYY CLOUD CHAMBER I M vALvEAGSSEMBLY DAYMGHT RANGE 19 7 CHANGE CN MEASURING CIRCUIT 7 5 SEC ALARMALARM a DELAY SIGNAL MALFUNCT'ON ZONE IDENTIFICATION RELAY CIRCUITRYINVENTOIS FREDERICK A. LUDEWIGJ! FRANK W. VAN LUIK,JR.

ATTOIIN EV PAIENIEBJuL 18 I972 3, 5 7 4 8 7 SHEET 2 BF 3 II5V 60- PA-J35 AWN VAC.

PUMP

ROTARY E VALVE A ASSEMBLY 5% CAM SWITCH MOTOR ALARM SIG. y K2 CLOSED IWHEN 555g A W. bfif owsn A A, 7 SUPPLY INVENTORQ FREDERICK A. LUDEWiQIRFRANK W VAN LU!K,JR.

av Q) ATTORNEY MUL'I'I-ZONEINCIPIENT OR ACTUAL FIRE AND/OR DANGEROUS GASDETECTION SYSTEM BACKGROUND OF INVENTION 1. Field Of Invention Thisinvention relates to a new and improved multi-zone incipient or actualfire and/or dangerous gas detection system.

More specifically, the invention relates to a multi-zone incipient oractual fire detection system employing a condensation nuclei particledetector as the sensor device, and which can be readily adapted also todetect accumulations above a certain safe level of certain dangerousgases (such as combustible hydrocarbon gases), and to signal theexistence of such incipient or actual fire or accumulation of dangerousgases to a central monitoring point, fire protection agency, or thelike.

2. Background of Invention In large multi-floor buildings, manufacturingfacilities having different manufacturing areas, warehouse storagefacilities, and the like, the provision of suitable automaticallyoperating fire detection equipment has been a continuing problem. Insuch multi-station or multi-zone facilities, the provision of suitable,economically feasible, and sulficiently sensitive fire detectionprotection becomes a problem because of the differing characteristics ofthe many different zones of the facility or area to be protected. Mostof the known multizone fire detection systems employ a plurality ofsensors with at least one (and sometimes even more) sensors beingprovided for each zone to be protected. In such arrangements, the use ofextremely sensitive sensor devices becomes prohibitive due to escalatingcosts. Hence, the provision of satisfactory muIti-zone, automaticallyoperating fire protection equipment thus far has been restricted to onlya few facilities where the extremely high cost of such a system isjustified by the need for the improved protection. To overcome thisproblem and to provide a relatively low cost, extremely sensitive fireand/or gas accumulation detection system for multi-zone facilitieswherein each of the different zones being protected presents differentbackground condition with respect to which the sensor must operate, thepresent invention was devised.

SUMMARY OF INVENTION It is therefor a primary object of the invention toprovide a new and improved multi-zone incipient or actual fire and/ordangerous gas detection system capable of use in multi-zone facilitieswherein the several zones being protected have different backgroundcharacteristics.

Another object of the invention is to provide such a system whichemploys a single, common, highly sensitive condensation nuclei particledetector as the sensing device of the detection system, and whichsequentially is applied to monitor the atmospheres of the severaldifferent zones of a multi-zone facility. For this purpose a relativelylow cost piping system and sequentially operated selector valve assemblyis used to gather atmospheric samples from each of the several zonesbeing monitored, and supplies the sample atmospheres sequentially to thecommon condensation nuclei detector. To overcome the problem ofdifferent background levels of activity or other factors affectingbackground conditions in each of the several zones being protected, thesensitivity of the condensation nuclei detector is individually adjustedin synehronism with the switching of the detector to analyze samples ofthe respective zones by the selector valve assembly in a manner so as tocompensate for the different background conditions of each of therespective zones being monitored.

Another object of the invention is to provide a detection system havingthe above characteristics wherein samples of the atmospheres of therespective zones being monitored are drawn off continuously and aresequentially sampled-on-thefly by the central selector valve assembly,and supplied to the common condensation nuclei detector for measurement.As a result, the system is made to be relatively fast responding to theoccurrence of an alarm condition in any of the zones being monitored.

In practicing the invention, a multi-zone detecting method and system isprovided for monitoring a plurality of different zones for the detectionof incipient or actual fires andlor dangerous gas accumulation. In thissystem samples of the atmosphere of each zone being monitored arecontinuously drawn off and sequentially supplied to a common measuringstation. At the common measuring station the sequentially suppliedsamples are analyzed by a condensation nuclei detector which signals theexistence of an alarm condition in any of the zones being monitored. Toprovide for different background conditions in the several zones beingprotected, the sensitivity of the common condensation nuclei detector isindividually adjusted sequentially in synchronization with the supply ofthe sample atmospheres as measurement is switched from one zone toanother in order to accommodate the individual background conditionsexisting in each zone to be monitored. Additionally, the commoncondensation nuclei detector is in effect desensitized for a shortduration settling period following each sequential switching of a sampleatmosphere being measured whereby the condensation nuclei detector willhave the sample of a previous zone cleared out and be conditioned torespond only to the newly supplied sample atmosphere. By including gasconversion devices in the input to the condensation nuclei detectorthrough which the sample atmospheres are caused to pass, the system canbe made to respond to accumulations of certain gases above a desiredlevel within any of the respective zones being monitored.

It is preferred that the sample atmospheres from all of the zones beingmonitored, be drawn off continuously and supplied to the common samplemeasurement station where they are sequentially accessed onthe-fly andmeasured in a predetermined sequential order so as to improve theresponse time of the monitoring method and system to an alarm conditionoccuring in any of the zones being monitored. By providing a centrallylocated, common selector valve assembly for sequentially supplying thesample atmospheres to the common condensation nuclei detector, separateadjustment of the flow rates of the respective sample atmosphere can bereadily accomplished to thereby accommodate differences in length ofpiping systems, diflerent diameters, etc and maintain a balanced flowrate from all of the zones being monitored to the central condensationnuclei detector. Additionally, by appropriate design of the centrallylocated selector valve assembly, the sampling rate andlor the durationof sampling of certain zones with respect to others can be readilymodified to accommodate the requirements of particular installations. Anadditional feature, is the provision of means for adjusting thesensitivity of the sample measurements in accordance with the time ofday and nature of operation being conducted in the respective zoneswhere such operations, level of activity, etc change in accordance withthe time of day.

A further desirable feature is the provision of fail-safe relay operatedindicating means for each of the several zones being monitored by thedetecting system for indicating the existence of an alarm condition inany of the zones being monitored in a fail-safe manner; the provision ofa fail-safe malfunction detector responsive to the output from thecommon condensation nuclei detector for indicating the existence of amalfunction condition in a fail-safe manner; and, the use of a highlysensitive, single common condensation nuclei detector as the sensingdevice and which has only relatively small electric power requirementswhereby the entire detection system can be operated on standby batterypower during emergency periods of power failure.

BRIEF DESCRIPTION OF DRAWINGS These and other objects, features and manyof the attendant advantages of this invention will be appreciated morereadily as the same becomes better understoody by reference to thefollowing detailed description when considered in connection with theaccompanying drawinm, wherein like parts in each of the several figuresare identified by the same reference character, and wherein:

FIG. 1 is a functional block diagram of an overall fire and/or gasdetector constructed in accordance with the invention;

FIG. 2A is a detailed electrical circuit diagram showing theconstruction of a part of one embodiment of the invention; and

FIG. 2B is a detailed electrical circuit diagram showing theconstruction of the remaining portion of the embodiment of the inventionshown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 is a functionalblock diagram of a new and improved multi-zone incipient or actual fireand/or dangerous gas detection system. The system is designed to providefire and dan gerous gas protection for multi-zone area such as thatindicated at 11 in FIG. 1. The multi-zone area 11 may comprise awarehouse having different storage rooms, a manufacturing facilityhaving different operations carried out in different rooms, amulti-story, multi-rm high rise apartment or office building, a schoolbuilding, or other similar installation having a plurality of zonesindicated as zones 1-4. The invention is in no way restricted toemployment with only four zones but may be expanded or contracted toaccommodate any desired number of zones by appropriate design of thesampling system (as described hereinafter to accommodate the particularnumber of zones to be protected. Each zone of the overall area orfacility 11 to be monitored in turn may be broken down into a pluralityof sampling areas. For example, there may be four sampling areas foreach zone as shown in FIG. 1. With such an arrangement, each samplingarea of a particular zone could correspond to an office suite with allof the ofiice suites on a particular floor of a multi-floor buildingbeing combined together into one zone, and with the remaining floorscomprising the remaining zones to be monitored. Other similararrangements for warehouses, manufacturing facilities, school buildings,and the like will be suggested to those skilled in the art.

In order to monitor each of the zones 1-4, a sampling system is providedwhich is comprised by a plurality of main sampling system conduitsIla-12d for each of the zones 1-4, respectively. The conduits 12a-l2dmay be formed from aluminum copper, galvinized steel, plastic or anyknown suitable piping for physically transporting sample gases from theat mospheres in each of the zones to a commonly located detector to bedescribed hereinafter. For this purpose, each of the conduits l2a-l2dare connected to header or manifold ducts that in turn are connectedthrough a plurality of branch conduits and intake heads l3a13d" tosample the several respective sampling areas within a particular zone.It is preferable that the individual intake heads 13 for each samplingarea be provided with a flow adjusting valve for balancing the flow fromall of the branch conduits into the main conduit for the zone, such as120 for example, whereby representative sample of all of the areaswithin a zone being monitored, is assured. Additionally, the intakeheads 13 may be different in size to accommodate particular installationrequirements.

To provide for a positive flow of sample gases from the intake heads13a-l3d', all of the main sample conduits 124-12 are connected to a maincommon exhaust conduit 14 that is exhausted through an air samplingblower 15 such as a centrifigal fan of conventional construction forexhausting the sample gases out into the atmosphere. Flow into the mainexhaust conduit 14 place through respective ones of a plurality of lowadjusting valves Al, A2, A3 and A4 for each of the respective zones 1-4.The flow adjusting valves AlA4 are all mounted at a common location andcomprise a part of a rotary valve assembly 16 which preferably is of thetype described in copending United States patent application Ser. No. 113,258 entitled Fluid Sampling Valve by Frederick A. Ludewig, .lr.,inventor filed Feb. 8, I971 concurrently with this applica tion andasigned to the Environment/One Corporation.

The flow adjusting valves Al-A4 provide centrally disposed, easilyaccessible means for adjusting the flow through each of the mainsampling conduits Ila-12d in a manner such that flow from all of thezones is balanced. That is, by restricting the flow through 12a, whichfor example may involve only a short run of conduit, the flow throughthis supply conduit can be made to equal that through 124', for example,which may be longer in length or a smaller diameter pipe due to therequirements of the particular zones in which the sampling system isinstalled. As a result of this arrangement, a continuous, balanced andsubstantially equal flow can be made to take place through all of themain supply conduits Ila-12d or a specific flow inbalance to achieve thedesired response times, by means of the respective zone flow adjustingvalves Al-A4. This flow is drawn through the main exhaust conduit 14 outthrough the blower 15 in a continuous manner whereby the atmosphere ofall the protected areas of each zone being monitored are continuouslysupplied to a central location where they can be sampled and monitored.

Samples of the atmospheres from each of the zones l-4 selectively areobtained through resp ctive ones of a plurality of selector valves Vl-V4comprising a part of the selector valve assembly 16. The selector valvesVl-V4 sequentially are opened to draw off on-the-fly portions of thesample atmospheres flowing in each of the main sample conduits l2a 12d,and selectively supply each of the respective samples through a main orcommon supply conduit 1'7 to the input of a common, highly sensitivedetector. The common, highly sensitive detector preferably comprises acondensation nuclei monitor having an input humidifier, cloud chamberand valve assembly 18. The humidifier, cloud chamber and valve assembly18 serve to humidify and expand the sample atmospheres suppliedselectively through the respective selector valves Vl-V4 and common main17 to a suitable degree of super saturation to cause water dropletformation about condensation nuclei particles entrained in the sampleatmospheres as centers of water droplet growth. The resultant cloud ofwater droplets produces a scattering effect on a light beam measuringcircuit 19 that in turn can activate the alarm and malfunction relaycircuitry 21. The common, condensation nuclei detector comprised bycloud chamber 18 and the measuring circuit I9 may be of the typedisclosed in US. Pat. No. 2,684,008, issued July 20, I954 or in US. Pat.No. 336,210 issued Jan. 4, I972. However, the measuring circuit 19preferably comprises an improved measuring circuit disclosed incopending United States patent application Ser. No. l 13,56l filed Feb.8, l97l entitled Improved Condensation Nuclei Monitor Measuring Circuit,George F.Skala, Inventor filed concurrently with this application, andassigned to the Environment/One Corporation.

For a more detailed description of the construction and operation of thecondensation nuclei cloud chamber and valve assembly 18 and measuringcircuit 19, reference is made to the aboveidentified issued US. patentand copending applications. Briefly, however, the cloud chamber andvalve assembly 18 first causes the sample gaseous atmospheres suppliedfrom the respective selector valves Vl-V4 to be humidified tosubstantially 100 percent relative humidity in a suitable humidifyingdevice. The humidified sample gaseous atmosphere then is supplied to anexpansion chamber where it suddenly is expanded to cause condensation ofwater droplets about nuclei particles entrained in the gaseousatmospheres as centers of condensation. The cloud of water droplets thusformed then is measured by a suitable light beam-photo cell arrangementwhich measures the amount of light scattered by the cloud formation ofwater droplets. Since the number of water droplets formed will bedetermined by the number or concentration of condensaion nucleiparticles entrained in the sample gaseous atmospheres, the amount oflight scattered by the cloud formation will be proportional to theparticle concentration. The proportional output signal derived by thecondensation nuclei measuring circuit 19 then is employed to operate thealarm and malfunction relay circuitry 21 in a manner to be describedmore fully hereinafter in connection with FIG. 2 of the drawings. Inorder to cause a positive flow of the sample gases through thehumidifier cloud chamber and valve assembly 18, a vacuum pump 22 isemployed in a known manner.

In operation, the air selector valve assembly 16 and air sampling blowerprovide continuous air flow from all sampling areas through intakes 13of all four zones of the facility 11 being monitored. Balanced flow fromall sampling areas in each zone is provided by intakes l3 and the zoneair flow adjusting valves Al-A4 provide means to equalize the flow fromall zones to accommodate different pressure drops due to differing tubelengths and/or tube diameters that comprise the supply conduits l2a-l2d.The selector valves Vl-V4 are normally closed and are automaticallysequentially opened one at a time by a motor driven cam assemblycomprising a part of rotary selector valve assembly 16 that alsooperates a plurality of cam operated switches 23. The cam operatedswitches 23 condition the CN measuring circuit 19 and alarm andmalfunction relay circuitry 21 for operation in connection with therespective samples from each of the zones. With this arrangement, as aparticular selector valve (such as V1) selectively is opened to allow asample from its zone (zone 1) to be drawn into the humidifier, cloudchamber and valve assembly 18, an associated cam operated switch 23 willappropriately adjust the sensitivity of the CN measuring circuit 19 andalarm and malfunction relay circuitry 21 to condition these circuits forthe individual background conditions existing in the zone being sampled(zone 1). Each of the remaining selector valves V2-V4 and theirassociated cam operated switches 23 function in a similar manner uponthe automatic sequential sampling of each of the remaining zones.

It is now a well known fact that fire and other combustion processesleading up the break out of an open flame, produces large quantities ofcondensation nuclei particles. The production of such large quantitiesof condensation nuclei particles takes place well in advance of even theoccurrence of smoke so that by sensing these small condensation nucleiparticles, an incipient fire can be detected often in advance of thebreakout of an open flame. With the present system due to the continuousonthe-fly sampling of the continuously flowing samples drawn off fromthe atmospheres of each of the zones 1-4 being protected, and due to thefast responding, highly sensitive measurement of the condensation nucleiparticle count in the sample atmospheres, fast sampling rates of evenlarge multi-zone facilities can be provided, and incipient and/or actualfire occurring in any part of the zones being monitored can be detectedand signaled to a central monitoring agency such as a local firedepartment within seconds of the development of an alarm condition.

It is now well known that the condensation nuclei detector is a highlysensitive, fast responding instrument which can detect extremely smallcondensation nuclei particles in the air even in very low concentrationswithin milliseconds. In the present system, the time limitation onsampling rate is introduced primarily by the sampling system. With thec0ntinuously flowing sample system described above, using /2 inchdiameter tubing and a commercially available blower fan is capable ofdrawing about 15 inches of water, sample atmospheres from even the mostremote zone of a large multizone facility can be transported to thecentrally located sampling valve assembly 16 within about 30 seconds.Because of the short run from the rotary sample valve 16 to cloudchamber and valve assembly 18, and the fast response of the condensationnuclei monitor, no more than 2 seconds are required to monitor aselected sample supplied from valve 16. Thus, with a four zone system,each zone can be monitored every 8 or 10 seconds so that an alarmcondition can be sensed and signalled within no more than 40 seconds ofits occurrence anywhere within the four zone facility being protected.

In any practical installation with which the present detection system isemployed, the background conditions in each of the zones will vary,sometimes quite widely. For example, consider that zones 1, 3 and 4 aremade up primarily of classrooms on different floors of a multi-levelschool building.

Then consider that zone 2 is comprised of the furnace room in which theboiler heating the school is located. Because of the differentcharacteristics of the two zones, the normal or background level ofcondensation nuclei particles entrained in the atmosphere of zone 2where the furnace is located will be substantially higher (greaterconcentration of condensation nuclei particles) due to the combustionprocesses taking place in the furnace and leakage outside the furnacelining. ln normal classroom activities, no such high background level ofcondensation nuclei particles will be produced by the activitiesundertaken in the classrooms. This is particularly true of study rooms.However, with respect to laboratories, the background activity again maybe much higher than that encountered in an average study classroom.Accordingly, some means must be provided for adjusting the sensitivityof the common, condensation nuclei detector measuring circuit l9 andalarm and malfunction relay circuitry 2], as the condensation nucleidetector is switched from one zone (such as zone 1) to the next zone(zone 2) for monitoring purposes. To provide such adjustment the camoperated switches 23 supply zone identification signals to both the CNmeasuring circuit 19 and the alarm and malfunction relay circuitry 21 tocondition these circuits for operation in conjunction with thebackground conditions existing in a particular zone being monitored atthat point in time by the condensation nuclei detector.

In addition to the above factors it can be appreciated that thebackground condensation nuclei particles produced in a classroom duringdaytime with students present in the room generally will be considerablyhigher than will be produced with no humans present in the room beingmonitored. Because of this time-dictated difference in background levelin activity, a day-night range change circuit feature indicated at 24 isprovided for again changing the sensitivity of the CN measuring circuit19 for different time periods occurring over a normal 24 hour timeperiod. The manner in which this adjustment is accomplished will beappreciated more fully hereinafler fol lowing a description of FIG. 2.

In addition to use as an incipient or actual fire detector, the systemof FIG. 1 also can be employed to detect accumulations of dangerousgases, such as combustible hydrocarbon gases and the like, by suitablemodification to include a filter and gas conversion unit shown at 25 inthe input to the humidifier, cloud chamber and valve assembly 18. Forthis purpose, cut-off valves shown at 26a and 26b and bypass valvesshown at 270 and 27b may be included in the common, main supply conduit17 on the input of the cloud chamber and valve assembly 18. By closingthe cut-off valves 26a and 26b and opening the bypass valves 27a and271;, the filter and gas conversion unit 25 may be included in thedetection system for monitoring the several zones being protected forthe presence of accumulation above a preset level of certain knowndangerous gases such as combustible hydrocarbon gases. The gasconversion unit 25 may comprise any known gas conversion unit such asare described in US Pat. No. 3,204,449, issued Sept. 14, I965 F.W. VanLuik, .lr., Inventor Detection and Measurement Of Organic Vapors AndGases," the Process And Apparatus For Detecting Gas" described in U.S.Pat. No. 3,l98,72l issued Aug. 3, 1965 to T.A. Rich; US. Pat. No. 3,]17,841 F.W. Van Luik, Jr. et al inventor issued Jan. 14, 1964 for Methodand Apparatus For Detecting Gases 0r Vapors;" US. Pat. No. 3,094,392G.F. Skala lnventor issued June 18, 1963 for Gas Detection," or patentnumber 2,897,059 issued July 28, I959 F.W. Van Luik, Jr., inventorProcess And Apparatus For Gas Detection.

lf desired, the system can be modified so that the gm conversion unit 25automatically is inserted in the sample flow portion of the systemsequentially as each zone is sampled and measured. With suchmodification, during each zone measure ment interval, the zone first ismonitored for incipient or actual fire conditions and then sequentiallyis measured for the existence of undesired gas accumulations beforeswitching the monitor to the next zone. For this purpose the cam designof the air selector valve and switching cam of selector valve assembly16 would be appropriately modified to provide for automatic andsequential actuation of the cut-ofi' and by pass valves 26a, 26b, 27a,27b in addition to valves Vl-V4. Because, the air selector valve andswitching cam assembly 16 is a centrally located unit along with thecentrally located, condensation nuclei detector assembly 18 and I9 andalarm and malfunction relay circuitry 21, such modification of the camdesign to include automatic gas sensing readily can be accomplished.Additionally, if due to the nature of one of the zones it should bemonitored more frequently or for longer periods than other zones, thecam design readily can be modified to provide a higher rate of samplingof the atmosphere of the particular zone, or an extended sampling periodof the zone relative to the sampling periods of the other zones. Becauseof the central location and easy accessibility of the air selector valveand switching cam assembly 16, such modification to accommodate theneeds of the particular installation readily can be accomplished.

From the preceding discussion it will be appreciated that irrespectiveof whether the condensation nuclei particles are supplied directly fromthe zones being monitored through the respective selector valves Vl-V4and valve 26a, 26b, or alternatively are produced in the gas conversionunit 25, they will be detected in the cloud chamber and valve assembly18 and readout by the measuring circuit 19. When the output signal fromthe measuring circuit 19 exceeds a preset maximum reference value, arelay for the particular zone in question will be deenergized causing analarm signal to be initiated. Additionally, should the readout from CNmeasuring circuit drop below a preset minimum value, a malfunction relaywill become deenergized and cause an alarm signal to be initiated. Forthis purpose fail-safe relay actuated alarms for both the zoneindicators and the malfunction indication, are employed.

The cams that operate the selector valves Vl-V4 and respective camoperated switches 23 for each of the zones 1-4 also allows the properzone alarm relay to become deenergized when an alarm condition issignaled. in addition, the cam operated switches 23 provide a momentarydesensitization of the alarm and malfunction relay circuitry 21 duringthe interval of switching from one zone to another. This desensitizationwhich may occur for example, over a five second, adjustable delay periodbefore an alarm condition can be signaled by any of the zone indicatorsimmediately aher switching the input of the CN monitor to a new zone.This pro vides adequate time for flushing out the sample from a previous(perhaps dirtier and hence higher background particle count) zone beforeaccepting an alarm condition signal from the next succeeding zone beingcurrently sampled which may have a lower background particle count dueto cleaner conditions. Thus, for example, as one switches from zone 2which may be a furnace room having a high condensation nuclei particlebackground count to zone 3 which may be a relatively clean classroomarea, it normally would be expected that zone 3 would have aconsiderably lower background condensation nuclei particle count. Forthis reason, the above mentioned change in sensitivity of the CNmeasuring circuit 19 is required as monitoring proceeds from one zone tothe next; however, in addition to the delay period before enabling thezone 3 alarm indicator, is required in order to allow time for thehigher background count zone 2 sample to be completely flushed outbefore allowing an alarm condition to be signaled by the new adjustmentin sensitivity to accommodate background conditions in zone 3.

The output of both the zone alarm and the malfunction relay circuitry isa separate relay closure for either zone alarm or a malfunctioncondition. Since fail-safe (normally energized) relays are employed,contact closure occurs upon the relay dropping out for either an alarmof malfunction condition (such as loss of power supply) although the twoconditions are separately read out. The contact closure can be used toinitiate remote as well as local alarm devices such as lights, bells,sirens or telephone dialers for dialing a message to the local firedepartment, etc.

In addition to the above listed features, flow detectors such asindicated at 28a, 28b, 28c and 28d may be included in each of the zonesample supply conduits Ila-12d, respectively, for sensing the flow ineach respective supply conduit. With this arrangement should the sampleflow from a given zone drop below a present value, a malfunctioncondition would be signaled for that particular zone.

FIG. 2 is a detailed schematic circuit diagram showing the constructionof the alarm and malfunction relay circuitry and its relation to thecondensation nuclei measuring circuit 19. As stated above the details ofthe condensation nuclei detector and the measuring circuit 19 aredisclosed more fully in US patent number 2,684,008 and in copendingSltala application Ser. No. 113,561 filed February 8, 1971 filedconcurrently herewith, and for a detailed description of theconstruction and operation of the CN measuring circuit 19, reference ismade to this copending application. Briefly, however, the CN measuringcircuit is excited from a direct current power supply 31 that in turnderives its power from a source of conventional l 15 volt, 60 cycle, l5amp residential or commercial alternating current power supply. The samea.c. supply also excites the vacuum pump 22 for periodically evacuatingor expanding the cloud chamber of the condensation nuclei detector in awell known manner, the rotary valve assembly l6 and cam switch motor 23.Since the rotary valve assembly 16 and cam switch motor 23 are excitedfrom the same power source, they will be operated in synchronism. Inoperation, the rotary valve assembly 16 sequentially and automaticallysupplies samples of the atmospheres of each of the zones 1-4 beingmonitored to the cloud chamber of the condensation nuclei detector whereit is humidified and expanded. Condensation nuclei particles present inthe sample produce a cloud of water droplets which in turn produce anattenuation effect on a light beam. This results in modulating the lightsignal impinging upon a photo cell detector shown at 33 in a well knownmanner. The photo cell detector 33 converts the light modulated signalinto an electric signal representative of the parti cle concentration ofthe condensation nuclei particles present in the sample atmospheres ofeach of the zones. This electric output signal then is amplifiedselectively in accordance with the background conditions of the zonebeing monitored, and supplied to an output signal level sensing aparticle count present in any of the sample atmospheres abovepredetermined reference level, as described more fully in the abovereferenced copending Skala application Ser. No. l l 3,56! filed Feb. 8,I971.

As each zone is monitored, the sensitivity of the CN measuring circuitis adjusted for the particular background conditions existing in thezones sequentially and synchronously with the sampling of theatmospheres from each of the zones by the rotary valve assembly. Forthis purpose, the rotary valve assembly l6 and cam switch motor 23 areoperated synchronously so that as the rotary valve assembly 16 suppliesa sample atmosphere for one of the zones (for example zone 1) the camswitch motor 23 simultaneously closes a cam operated switch(S3A) foradjusting the sensitivity of the CN measuring circuit 19 to correspondto the background conditions existing in that zone. In the examplecited, the cam operated switch contacts 83A are closed so as to connecta feedback resistor R1 in the feedback path of an operational amplifierincluded in the CN measuring circuit 19 to thereby adjust the gain ofthe CN measuring circuit 19 to correspond to the background conditionsexisting in zone I. In a similar manner, cam operated switch contacts54A, SSA and S6A connect in the difierent value resistors R2, R3 or R4selectively for adjusting the gain of the output amplifier in accordancewith the background conditions for zones 2-4.

In addition to the above described feature, a second set of contactsshown as DN-l selectively are closed by operation of the time actuatedday-night range change circuit 24 shown in FIG. I. This further adjuststhe gain of the output amplifier in CN measuring circuit 19 to thedifierent conditions existing at nighttime for the zone 2 area. Forexample, if zone 2 is a manufacturing area, then the presence of a largenumber of people (some of whom may be smoking cigarettes) in themanufacturing facility during the daytime would require that the gain ofthe amplifier be adjusted to a relatively low value during the daytime.However, at night it would be desirable to increase the gain of theoutput amplifier to a correspondingly higher level due to absence of thehuman activity during the night interval. The DN-l contact andassociated RN resistor allows for this day and night adjustment fordiffering conditions in zone 2. Similar arrangements can be made for anyother of the zones where different activities are involved duringdifferent time periods of the day.

In addition to selectively adjusting the gain of the CN measuringcircuit 19 in accordance with the zone being sampled, the cam actuatedswitch arrangement also operates selectively to open one of the normallyclosed contacts of a plurality of switches 838468 in the alarm andmalfunction relay circuitry 21. The function of the cam actuatednormally closed contacts S3B-S6B will become more apparent in the lightof the following description of the alarm and malfunction relaycircuitry 21.

Under normal conditions in all of the zones where normal backgroundparticle count signals are derived and do not exceed the alarm level,the switch contacts K2 of a level sensing relay in the CN measuringcircuit 19 will be maintained closed. Under these conditions, the K5solenoid winding in relay circuitry 21 will be energized causing all ofthe K5 contacts to be closed. The alarm and malfunction relay circuitryis energized from a pair of ac. power supply terminals 35 and 36connected through suitable fusing and master on-off switch (not shown)with the terminal 36 being split into a pair of branch power supplyterminals 360 and 36b. Under normal, non-alarm conditions with the K2contacts closed in CN measuring circuit 19, the K5 solenoid winding willbe connected directly across power supply terminals 35 and 36A so as tocause all of the K5 contacts to be maintained closed under theseconditions. The K5 contacts are connected in series circuit relationshipwith respective ones of the solenoid windings K6-K9 and the K10 contactsof a reset relay whose actuating winding is connected directly betweenthe power supply terminals 35 and 36A through a reset button 37. Thus,under non-alarm normal conditions with the K2 and K5 contacts closed asdescribed previously above, closure of the reset push button switch 37will excite the K10 reset solenoid winding causing the K10 contacts tobe closed thereby energizing all of the K6-K9 solenoid windings.

Each of the K6-K9 relays has two sets of normally closed contacts andone set of normally open contacts (normallyopen or normally-closed inthe non-erngized condition) so that upon being energized, the normallyopen contacts will be closed and the normally closed contacts will beopened. Thus, it will be seen that in the case of the K6 relay (which isassumed to represent zone I) the normally open K6 contacts will beclosed and will establish a holding circuit between the power supplyterminals 35 and 36A, through the now closed" normally-open K6 contacts,the K6 winding and the closed K5 contact due to the continuedenergization of the K5 winding through the K2 contacts in the CNmeasuring circuit 19. Similar holding circuits can be traced through foreach of the remaining zones 2-4 represented by windings K7-K9respectively.

An alarm condition in any one of the zones being monitored is signaledby turn-on of one of the signal lamps 1-4 mounted on a suitablemonitoring panel at a central control station. The lamps 1-4 areconnected in series circuit relationship between the power supplyterminals 368 and 35 through the normallyclosed contacts K6-K9,respectively, which in the energized condition of the K6-K9 relay willbe maintained open. Thus, under normal, non-alarm conditions the lampsare not lighted. The cam actuated switch contacts S3B-S6B are connectedbetween the power supply terminal 36b and the juncture of the K6-K9relay windings with their respective associated KS contacts. The camactuated switch contacts S3B-S6B are maintained normally closed but areselectively opened sequentially with the supply of a sample atmospherefrom the zone they are associated with to the cloud chamber of thecondensation nuclei detector.

With the above described arrangement, should an alarm condition bedetected due to an excessive concentration of condensation nucleiparticles, the K2 contacts in the CN measuring circuit 19 will open. Asa consequence, the K5 relay winding is deenergized thereby allowing allof the K5 contacts to open. Upon this occurrence (assuming zone 1 isbeing sampled), the remaining solenoid windings K7-K9 will continue tobe energized through the normally-closed cam actuated switch contactsS4B-S6B despite the fact that there associated K5 contacts have opened.However, in the case of the zone being sampled (in this case zone I),its normally closed contacts will be open due to the cam actuation atthe time of sampling. As a consequence, the K6 relay winding will dropout, allowing its normally-open K6 contact to open, and itsnormally-closed K6 contacts to close. This in turn lights lamp 1 therebyindicating to the monitoring station that an alarm condition exists inzone t.

In addition to the local indication of the alarm condition due tolighting lamp 1, a parallel connected array of normally closed contactsK6-K9 shown in the upper portion of alarm and malfunction relaycircuitry 21 will cause an output indication of the alarm condition tobe supplied over an additional set of output lines. This additionaloutput indication can be used to actuate remote indicating equipment, analarm in a local fire department, a dial telephone message, or toactuate some other similar apparatus indicative of the existence of thedetected alarm condition. Because of the parallel connection of therelay contacts, the remote indication will not identify in which zonethe alarm condition exists, but will only be indicative of an alarmcondition existing in one of the zones of the overall facility beingmonitored. Further, from the above description, it will be appreciatedthat the alarm circuitry is connected in a fail-safe manner. That is tosay, the alarm relays must be energized to be in a safe (normal),non-alarm condition. Thus, in the event of a component failure, burnout,or the like, an alarm condition will be signaled indicating that theequipment must be checked.

in addition to the alarm relay circuitry, malfunction relay circuitry isprovided for indicating the existence of a power failure, failure of thecondensation nuclei detector due to low water in the humidifier, or somesimilar condition. For this purpose, a K4 relay winding is connectedbetween power supply terminals 364 and 35 through the normally open K3contacts of a minimum signal level sensing relay also included in the CNmeasuring circuit 19. The K3 contacts of the minimum signal levelsensing relay in CN measuring circuit 19 will be maintained closed forso long as the particle count derived by the condensation nucleidetector remains above a reference, minimum level. it is wellestablished, that regardless of how clean a room or area is, there willalways be some predetermined number of condensation nuclei particlespresent in the atmosphere of the room. The presence of these normal,background levels of condensation nuclei particles can be used to signalthe existence of a malfunction condition. Accordingly, where theparticle count signal from the output of the condensation nucleidetector drops below this minimum particle count level, the K3 contactswill be caused to open. This in turn deenergizes the K4 windingresulting in the closing of a set of normally-closed K4 contacts thatconnect a malfunction lamp directly across power supply terminals 35 and36A. In addition, a set of normally open K4 contacts shown at the bottomof the alarm and malfunction relay circuitry 21 will be opened causing aremote indication of the malfunction condition to be transmitted to aremote indicating station.

From the foregoing description, it will be appreciated that the presentinvention provides a new and improved multi-zone incipient or actualfire and dangerous gas detection system. The system readily can beadapted to detect either incipient or actual fire and/or dangerous gasaccumulations above a certain safe level, and to signal the existence ofsuch alarm conditions to a central monitoring point as well as remotelysignaling to a local fire department, security agency or the like. Thesystem employs a single, common, highly sensitive condensation nucleiparticle detector as a sensor which sequentially is switched to monitorthe atmosphere of the several zones of a multi-zone facility beingprotected. This is accomplished through the medium of a relatively lowcost piping system and sequentially operated selector valve assemblyused to gamer atmospheric samples automatically from each of the zonesbeing monitored, and to supply the sample atmospheres sequentially tothe common CN detector. Dynamic adjustment for different backgroundlevels of activity in the several zones being monitored is provided forby adjusting the sensitivity of the CN detector synchronously with theswitching of the detector to monitor the several zones of the facilitybeing protected. ln addition, the detecting system employs acontinuously operating sample system which samples atmospheres from theseveral zones selectively on-the-fly so as to provide a relatively fastresponse to the occurrence of an alarm condition in any of the zonesbeing monitored. The entire system requires very little power drain andif need be can be operated from standby battery power sources andconverters during periods of emergency power failure.

Having described one embodiment of a new and improved multi-zoneincipient or actual fire and/or dangerous gas detection systemconstructed in accordance with the invention, other modifications andvariations of the invention will be suggested to those skilled in theart in the light of the above teachings. It is therefor to be understoodthat changes may be made in the particular embodiments of the inventiondescribed which are within the fully intended scope of the invention asdefined by the appended claims.

What is claimed is:

l. A multi-zone detecting system comprising a multi-zone sampling systemfor obtaining samples of the atmosphere of the respective zones beingmonitored and supplying the same to a common sampling station, a commondetector located at the common detection station for detecting theexistence of an alarm condition in any of the zones and deriving anoutput indication of the alarm condition, selective supply means coupledto the multi-zone sampling system and to the common detector forsequentially supplying the samples from the respective zones to thecommon detector, and sensitivity adjusting means coupled to the commondetector as it is sequentially switched from one zone to the nextwhereby the response of the detector is individually adjusted tobackground conditions existing in each zone being monitored.

2. A multi-zone detecting system according to claim 1 further includingmeans for desensitizing the common detector for a pre-determinedsettling time during each sequential switching of the input to thecommon detector whereby a short time interval settling period isprovided prior to monitoring the samples from each of the zones.

3. A multi-zone detecting system according to claim 1 wherein the commondetector comprises a condensation nuclei detector for detectingcondensation nuclei particles present in the atmospheres of therespective zones being monitored and for deriving an output indicationof the presence of condensation nuclei particles in excess of a givenbackground amount.

4. A multi-zone detecting system according to claim 3 further includinggas conversion means interposed in the input to the condensation nucleidetector for converting dangerous gases entrained in the sampleatmospheres from the several zones into condensation nuclei for supplyto the condensation nuclei detector.

5. A multi-zone detecting system according to claim 1 further includingtime-controlled sensitivity adjusting means for further adjusting thesensitivity of the common detector in accordance with a predeterminedtimed program whereby compensation can be provided for differentbackground conditions at different times such as different day and nightoperations in the zones being monitored.

6. A multi-zone detecting system according to claim 1 wherein theselective supply means comprises continuous flow supply means forproviding a continuous flow of the sample atmospheres from therespective zones being monitored, and selector valve means operable inconjunction with the continuous flow supply means for sequentiallyselecting omthe-fly from the continuous flowing streams samples of theatmospheres from the respective zones for supply to the common detectorwhereby response of the overall detecting system to an alarm conditionis speeded up.

7. A multi-zone detecting system according to claim 6 wherein saidselector valve means is a multiple input port rotary selector valvehaving a common output port and is located at the common samplingstation input valve and includes individually flow adjusting means foreach of the input ports whereby the continuous flow of sample atmospherefrom the respective zones being monitored can be individually adjustedto compensate for differences in length of flow path and the like tothereby balance flow of the sample atmospheres to the common detector.

8. A multi-zone detecting system according to claim 7 wherein the designof the selector valve means readily can be modified to accommodatedifferent sampling periods, multiple sampling of particular zones andthe like in accordance with the requirements of a particular multi-zoneinstallation to be monitored.

9. A multi-zone detecting system according to claim 8 further includingmeans for desensitizing the common detector for a predetermined settlingtime during each sequential switching of the input to the commondetector whereby a short time interval settling period is provided priorto monitoring the sample from each of the zones.

10. A multi-zone detecting system according to claim 9 wherein thecommon detector comprises a condensation nuclei detector for detectingcondensation nuclei particles present in the atmospheres of therespective zones being monitored and for deriving an output signalindicative of the presence of condensation nuclei particles in excess ofa given background amount, said condensation nuclei detector havingoutput signal amplifying means for amplifying the output signal andwherein said sensitivity adjusting means comprises gain change circuitmeans coupled to the output signal amplifying means for changing thegain of the output signal amplify ing means synchronously with theswitching of the zones being monitored whereby the sensitivity of thedetecting system is individually adjusted to background conditionsexisting in each zone being monitored.

H. A multi-zone detecting system according to claim 10 further includinggas conversion means selectively connectable to the input of thecondensation nuclei detector for converting dangerous gases entrained inthe sample atmospheres selectively supplied from the several zones intocondensation nuclei for measurements.

l2. A multi-zone detecting system according to claim 10 furtherincluding time controlled sensitivity adjusting means for furtheradjusting the sensitivity of the output amplifying means in accordancewith a predetermined time program whereby compensation can be providedfor different background conditions at different times such as differentday and night operations in the zones being monitored.

13. A multi-zone detecting system according to claim 10 furtherincluding flow sensing means disposed in the respective paths of thesampling system for sensing the respective flow rates and derivingoutput control signal in accordance therewith, and means supplying therespective control signals to the alarm circuitry to signal theexistence of a malfunction where the flow rates drop below predeterminedvalues.

14. A multi-zone detecting system according to claim 10 wherein themeans for desensitizing the common detector for a predetermined intervalof time during each sequential switching of the common detector tosample the respective zones being monitored comprises cam operatedswitch means operated synchronously with rotary selector valve forderiving a desensitizing electric signal that is applied to the commondetector to render it unresponsive to alarm conditions for apredetermined settling interval following each switching operation bythe rotary selector valve.

15. A multi-zone detecting system according to claim 14 furtherincluding failsafe relay operated indicating means for each of theseveral zones being monitored by the detecting system and responsive tothe output signal from the output signal amplifying means of thecondensation nuclei detector for indicating the existence of an alarmcondition in any of the zones being monitored in fail-safe manner.

16. A multi-zone detecting system according to claim 15 furtherincluding fail-safe malfunction indicating means responsive to theoutput of the condensation nuclei detector means for indicating theexistence of a malfunction in a failsafe manner upon the output from thecondensation nuclei detector means dropping below a predeterminedminimum reference level.

17. A multi-zone detecting system according to claim I further includingfail-safe malfunction indicating means responsive to the output from thecommon detector for indicating the existence of a malfunction conditionin any of the zones being monitored in a fail-safe manner upon theoutput from the common detector dropping below a predetermined minimumreference level.

18. A multi-zone detecting system according to claim I further includingflow sensing means disposed in the respective paths of the samplingsystem for sensing the respective flow rates and deriving output controlsignals representative of the respective flow rates, and means supplyingthe respective control signals to the common detector for adjusting thesensitivity of the common detector in accordance with the flow rate ofthe sample atmosphere supplied from the respective zones.

19. A multi-zone detecting system according to claim 1 further includingfail-safe relay operated indicating means for each of the several zonesbeing monitored by the detecting system and responsive to the outputfrom the common detector for indicating the existence of an alarmcondition in any of the zones being monitored in a fail-safe manner,fail-safe malfunction detector means responsive to the output from thecommon detector means for indicating the existence of a malfunctioncondition in the detecting system in a fail-safe manner, and wherein thecommon detector and indicating arrangement have relatively smallelectric power requirements whereby the entire system can be operated onstandby battery power during emergency periods of power failure.

20. A method of monitoring a plurality of different zones for thedetection of incipient or actual fires and/or dangerous gas accumulationcomprising sequentially supplying a sample of the atmosphere in eachzone being monitored to a common measuring station, measuring eachsample sequentially at the common measurement station to detect andsignal the existence of an alarm condition in any of the zones beingmonitored, and adjusting the sensitivity of each sample measurementsequentially in synchronization with the supply of sample atmospheres asmeasurement is switched from one zone to another in accordance with theindividual background conditions existing in each zone being monitored.

2]. A method according to claim 20 further including desensitizing thesample measurement for a short duration settling period following eachsequential switching of a sample atmosphere from one zone beingmonitored to the next.

22. A method according to claim 21 wherein the sample measurement isobtained by deriving a measurement of the condensation nuclei particleconcentration present in the sample gaseous atmosphere of each zonebeing monitored.

23. A method according to claim 22 further including converting gaseouscontituents entrained in the atmosphere of the zones being monitoredinto condensation nuclei particles whose concentration is representativeof the proportion of the gaseous contituents present in the atmosphereand then measuring the condensation nuclei particle concentration as anindication of the proportion of gaseous constituents entrained In thesample atmosphere.

24. A method according to claim 20 further including adjusting thesensitivity of the sample measurement in accordance with the time of dayand the nature of operations being conducted in the respective zonesbeing monitored where such operations change in accordance with the timeof day.

25. A method according to claim 20 wherein sample atmospheres from allof the zones being monitored are continuously drawn from each of therespective zones and supplied to the common sample measurement stationwhere the respective sample atmospheres are sequentially accessedon-the-fly and measured in a predetermined sequential order whereby theresponse time of the monitoring method to an alarm condition is greatlyimproved.

26. A method according to claim 25 further comprising separatelyadjusting the flow rate of the respective sample atmospheres to themeasuring operation in order to balance the flow rates and improveresponse of the measurement only to changes in conditions in the zonesbeing monitored.

27. A method according to claim 26 wherein the sampling rate and/or theduration of sampling of certain zones is different due to the differentnature of the zones being monitored.

28. A method according to claim 25 further including desensitin'ng thesample measurement for a short duration settling period following eachsequential switching of a sample atmosphere from one zone beingmonitored to the next.

29. A method according to claim 28 wherein the sample measurement isobtained by deriving a measurement of the condensation nuclei particleconcentration present in the sample gaseous atmosphere of each zonebeing monitored.

30. A method according to claim 29 further including converting certaingaseous constituents entrained in the atmosphere of the zones beingmonitored into condensation nuclei particles whose concentration isrepresentative of the proportion of the gaseous constituents present inthe atmosphere and then measuring the condensation nuclei particleconcentration as an indication of the proportion of the gaseousconstituents entrained in the sample atmospheres.

31. A method according to claim 29 further including ad justing thesensitivity of the sample measurements in accordance with the time ofday and the nature of operations being conducted in the respective zonesbeing monitored where such operation change in accordance with the timeof day.

32. A method according to claim 29 further including measuring theoutput from the condensation nuclei detector continuously and signalingthe existence of a malfunction condition upon the output dropping belowa predetermined minimum level.

33. A method according to claim 29 further including indicating theexistence of an alarm condition in any of the zones being monitored or amalfunction in a fail-safe manner whereby upon the occurrence of a powerfailure, malfunction or the like an output alarm is indicated.

34. A method according to claim 20 further including sensing the flowrate of the sample atmospheres from the dif ferent zones being monitoredand signalling a malfunction condition where the flow rate falls below apredetermined standard.

1. A multi-zone detecting system comprising a multi-zone sampling systemfor obtaining samples of the atmosphere of the respective zones beingmonitored and supplying the same to a common sampling station, a commondetector located at the common detection station for detecting theexistence of an alarm condition in any of the zones and deriving anoutput indication of the alarm condition, selective supply means coupledto the multi-zone sampling system and to the common detector forsequentially supplying the samples from the respective zones to thecommon detector, and sensitivity adjusting means coupled to the commondetector as it is sequentially switched from one zone to the nextwhereby the response of the detector is individually adjusted tobackground conditions existing in each zone being monitored.
 2. Amulti-zone detecting system according to claim 1 further including meansfor desensitizing the common detector for a pre-determined settling timeduring each sequential switching of the input to the common detectorwhereby a short time interval settling period is provided prior tomonitoring the samples from each of the zones.
 3. A multi-zone detectingsystem according to claim 1 wherein the common detector comprises acondensation nuclei detector for detecting condensation nuclei particlespresent in the atmospheres of the respective zones being monitored andfor deriving an output indication of the presence of condensation nucleiparticles in excess of a given background amount.
 4. A multi-zonedetecting system according to claim 3 further including gas conversionmeans interposed in the input to the condensation nuclei detector forconverting dangerous gases entrained in the sample atmospheres from theseveral zones into condensation nuclei for supply to the condensationnuclei detector.
 5. A multi-zone detecting system according to claim 1further including time-controlled sensitivity adjusting means forfurther adjusting the sensitivity of the common detector in accordancewith a predetermined timed program whereby compensation can be providedfor different background conditions at different times such as differentday and night operations in the zones being monitored.
 6. A multi-zonedetecting system according to claim 1 wherein the selective supply meanscomprises continuous flow supply means for providing a continuous flowof the sample atmospheres from the respective zones being monitored, andselector valve means operable in conjunction with the continuous flowsupply means for sequentially selecting on-the-fly from the continuousflowing streams samples of the atmospheres from the respective zones forsupply to the common detector whereby response of the overall detectingsystem to an alarm condition is speeded up.
 7. A multi-zone detectingsystem according to claim 6 wherein said selector valve means is amultiple input port rotary selector valve having a common output portand is located at the common sampling station input valve and includesindividually flow adjusting means for each of the input ports wherebythe continuous flow of sample atmosphere from the respective zones beingmonitored can be individually adjusted to compensate for differences inlength of flow path and the like to thereby balance flow of the sampleatmospheres to the common detector.
 8. A multi-zone detecting systemaccording to claim 7 wherein the design of the selector valve meansreadily can be modified to accommodate different sampling periods,multiple sampling of particular zones and the like in accordance withthe requirements of a particular multi-zone installation to bemonitored.
 9. A multi-zone detecting system according to claim 8 furtherincluding means for desensitizing the common detector for apre-determined settling time during each sequential switching of theinput to the common detector whereby a short time interval settlingperiod is provided prior to monitoring the sample from each of thezones.
 10. A multi-zone detecting system according to claim 9 whereinthe common detector comprises a condensation nuclei detector fordetecting condensation nuclei particles present in the atmospheres ofthe respective zones being monitored and for deriving an output signalinDicative of the presence of condensation nuclei particles in excess ofa given background amount, said condensation nuclei detector havingoutput signal amplifying means for amplifying the output signal andwherein said sensitivity adjusting means comprises gain change circuitmeans coupled to the output signal amplifying means for changing thegain of the output signal amplifying means synchronously with theswitching of the zones being monitored whereby the sensitivity of thedetecting system is individually adjusted to background conditionsexisting in each zone being monitored.
 11. A multi-zone detecting systemaccording to claim 10 further including gas conversion means selectivelyconnectable to the input of the condensation nuclei detector forconverting dangerous gases entrained in the sample atmospheresselectively supplied from the several zones into condensation nuclei formeasurements.
 12. A multi-zone detecting system according to claim 10further including time controlled sensitivity adjusting means forfurther adjusting the sensitivity of the output amplifying means inaccordance with a predetermined time program whereby compensation can beprovided for different background conditions at different times such asdifferent day and night operations in the zones being monitored.
 13. Amulti-zone detecting system according to claim 10 further including flowsensing means disposed in the respective paths of the sampling systemfor sensing the respective flow rates and deriving output control signalin accordance therewith, and means supplying the respective controlsignals to the alarm circuitry to signal the existence of a malfunctionwhere the flow rates drop below predetermined values.
 14. A multi-zonedetecting system according to claim 10 wherein the means fordesensitizing the common detector for a predetermined interval of timeduring each sequential switching of the common detector to sample therespective zones being monitored comprises cam operated switch meansoperated synchronously with rotary selector valve for deriving adesensitizing electric signal that is applied to the common detector torender it unresponsive to alarm conditions for a predetermined settlinginterval following each switching operation by the rotary selectorvalve.
 15. A multi-zone detecting system according to claim 14 furtherincluding fail-safe relay operated indicating means for each of theseveral zones being monitored by the detecting system and responsive tothe output signal from the output signal amplifying means of thecondensation nuclei detector for indicating the existence of an alarmcondition in any of the zones being monitored in fail-safe manner.
 16. Amulti-zone detecting system according to claim 15 further includingfail-safe malfunction indicating means responsive to the output of thecondensation nuclei detector means for indicating the existence of amalfunction in a fail-safe manner upon the output from the condensationnuclei detector means dropping below a predetermined minimum referencelevel.
 17. A multi-zone detecting system according to claim 1 furtherincluding fail-safe malfunction indicating means responsive to theoutput from the common detector for indicating the existence of amalfunction condition in any of the zones being monitored in a fail-safemanner upon the output from the common detector dropping below apredetermined minimum reference level.
 18. A multi-zone detecting systemaccording to claim 1 further including flow sensing means disposed inthe respective paths of the sampling system for sensing the respectiveflow rates and deriving output control signals representative of therespective flow rates, and means supplying the respective controlsignals to the common detector for adjusting the sensitivity of thecommon detector in accordance with the flow rate of the sampleatmosphere supplied from the respective zones.
 19. A multi-zonedetecting system according to claim 1 further including fail-safe relayoperated inDicating means for each of the several zones being monitoredby the detecting system and responsive to the output from the commondetector for indicating the existence of an alarm condition in any ofthe zones being monitored in a fail-safe manner, fail-safe malfunctiondetector means responsive to the output from the common detector meansfor indicating the existence of a malfunction condition in the detectingsystem in a fail-safe manner, and wherein the common detector andindicating arrangement have relatively small electric power requirementswhereby the entire system can be operated on standby battery powerduring emergency periods of power failure.
 20. A method of monitoring aplurality of different zones for the detection of incipient or actualfires and/or dangerous gas accumulation comprising sequentiallysupplying a sample of the atmosphere in each zone being monitored to acommon measuring station, measuring each sample sequentially at thecommon measurement station to detect and signal the existence of analarm condition in any of the zones being monitored, and adjusting thesensitivity of each sample measurement sequentially in synchronizationwith the supply of sample atmospheres as measurement is switched fromone zone to another in accordance with the individual backgroundconditions existing in each zone being monitored.
 21. A method accordingto claim 20 further including desensitizing the sample measurement for ashort duration settling period following each sequential switching of asample atmosphere from one zone being monitored to the next.
 22. Amethod according to claim 21 wherein the sample measurement is obtainedby deriving a measurement of the condensation nuclei particleconcentration present in the sample gaseous atmosphere of each zonebeing monitored.
 23. A method according to claim 22 further includingconverting gaseous contituents entrained in the atmosphere of the zonesbeing monitored into condensation nuclei particles whose concentrationis representative of the proportion of the gaseous contituents presentin the atmosphere and then measuring the condensation nuclei particleconcentration as an indication of the proportion of gaseous constituentsentrained in the sample atmosphere.
 24. A method according to claim 20further including adjusting the sensitivity of the sample measurement inaccordance with the time of day and the nature of operations beingconducted in the respective zones being monitored where such operationschange in accordance with the time of day.
 25. A method according toclaim 20 wherein sample atmospheres from all of the zones beingmonitored are continuously drawn from each of the respective zones andsupplied to the common sample measurement station where the respectivesample atmospheres are sequentially accessed on-the-fly and measured ina predetermined sequential order whereby the response time of themonitoring method to an alarm condition is greatly improved.
 26. Amethod according to claim 25 further comprising separately adjusting theflow rate of the respective sample atmospheres to the measuringoperation in order to balance the flow rates and improve response of themeasurement only to changes in conditions in the zones being monitored.27. A method according to claim 26 wherein the sampling rate and/or theduration of sampling of certain zones is different due to the differentnature of the zones being monitored.
 28. A method according to claim 25further including desensitizing the sample measurement for a shortduration settling period following each sequential switching of a sampleatmosphere from one zone being monitored to the next.
 29. A methodaccording to claim 28 wherein the sample measurement is obtained byderiving a measurement of the condensation nuclei particle concentrationpresent in the sample gaseous atmosphere of each zone being monitored.30. A method according to claim 29 further including converting certaingaseous constituents entrained in the atmospheRe of the zones beingmonitored into condensation nuclei particles whose concentration isrepresentative of the proportion of the gaseous constituents present inthe atmosphere and then measuring the condensation nuclei particleconcentration as an indication of the proportion of the gaseousconstituents entrained in the sample atmospheres.
 31. A method accordingto claim 29 further including adjusting the sensitivity of the samplemeasurements in accordance with the time of day and the nature ofoperations being conducted in the respective zones being monitored wheresuch operation change in accordance with the time of day.
 32. A methodaccording to claim 29 further including measuring the output from thecondensation nuclei detector continuously and signaling the existence ofa malfunction condition upon the output dropping below a predeterminedminimum level.
 33. A method according to claim 29 further includingindicating the existence of an alarm condition in any of the zones beingmonitored or a malfunction in a fail-safe manner whereby upon theoccurrence of a power failure, malfunction or the like an output alarmis indicated.
 34. A method according to claim 20 further includingsensing the flow rate of the sample atmospheres from the different zonesbeing monitored and signalling a malfunction condition where the flowrate falls below a predetermined standard.